Since then, 25m people have died from AIDS and another 34m are infected. The 30th anniversary of the disease’s discovery has been taken by many as an occasion for hand-wringing. Yet the war on AIDS is going far better than anyone dared hope. A decade ago, half of the people in several southern African countries were expected to die of AIDS. Now, the death rate is dropping. In 2005 the disease killed 2.1m people. In 2009, the most recent year for which data are available, the number was 1.8m. Some 5m lives have already been saved by drug treatment. In 33 of the worst-affected countries the rate of new infections is down by 25% or more from its peak.

Even more hopeful is a recent study which suggests that the drugs used to treat AIDS may also stop its transmission. If that proves true, the drugs could achieve much of what a vaccine would. The question for the world will no longer be whether it can wipe out the plague, but whether it is prepared to pay the price.

The appliance of science

If AIDS is defeated, it will be thanks to an alliance of science, activism and altruism. The science has come from the world’s pharmaceutical companies, which leapt on the problem. In 1996 a batch of similar drugs, all of them inhibiting the activity of one of the AIDS virus’s crucial enzymes, appeared almost simultaneously. The effect was miraculous, if you (or your government) could afford the $15,000 a year that those drugs cost when they first came on the market.

Much of the activism came from rich-world gays. Having badgered drug companies into creating the new medicines, the activists bullied them into dropping the price. That would have happened anyway, but activism made it happen faster.

The altruism was aroused as it became clear by the mid-1990s that AIDS was not just a rich-world disease. Three-quarters of those affected were—and still are—in Africa. Unlike most infections, which strike children and the elderly, AIDS hits the most productive members of society: businessmen, civil servants, engineers, teachers, doctors, nurses. Thanks to an enormous effort by Western philanthropists and some politicians (this is one area where even the left should give credit to George Bush junior), a series of programmes has brought drugs to those infected.

The result is patchy. Not enough people—some 6.6m of the 16m who would most quickly benefit—are getting the drugs. And the pills are not a cure. Stop taking them, and the virus bounces back. But it is a huge step forward from ten years ago.

What can science offer now? A few people’s immune systems control the disease naturally (which suggests a vaccine might be possible) and antibodies have been discovered that neutralise the virus (and might thus form the basis of AIDS-clearing drugs). But a cure still seems a long way off. Prevention is, for the moment, the better bet.

There are various ways to stop people getting the disease in the first place. Nagging them to use condoms and to sleep around less does have some effect. Circumcision helps to protect men. A vaginal microbicide (none exists, but at least one trial has gone well) could protect women. The new hope centres on the idea of combining treatment with prevention.

A question of money

In the early days scientists were often attacked by activists for being more concerned with trying to prevent the epidemic spreading than treating the affected. Now it seems that treatment and prevention will come in the same pill. If you can stop the virus reproducing in someone’s body, you not only save his life, you also reduce the number of viruses for him to pass on. Get enough people on drugs and it would be like vaccinating them: the chain of transmission would be broken.

That is a huge task. It is not just a matter of bringing in those who should already be on the drugs (the 16m who show symptoms or whose immune systems are critically weak). To prevent transmission, treatment would in theory need to be expanded to all the 34m people infected with the disease. That would mean more effective screening (which is planned already), and also a willingness by those without the symptoms to be treated. That willingness might be there, though, if it would protect people’s uninfected lovers.

Such a programme would take years and also cost a lot of money. About $16 billion a year is spent on AIDS in poor and middle-income countries. Half is generated locally and half is foreign aid. A report in this week’s Lancet suggests a carefully crafted mixture of approaches that does not involve treating all those without symptoms would bring great benefit for not much more than this—a peak of $22 billion in 2015, and a fall thereafter. Moreover, most of the extra spending would be offset by savings on the treatment of those who would have been infected, but were not—some 12m people, if the boffins have done their sums right. At $500 per person per year, the benefits would far outweigh the costs in purely economic terms; though donors will need to compare the gain from spending more on knocking out AIDS against other worthy causes, such as eliminating malaria (see article).

For the moment, the struggle is to stop some rich countries giving less. The Netherlands and Spain are cutting their contributions to the Global Fund, one of the two main distributors of the life-saving drugs (the other is Mr Bush’s brainchild, PEPFAR), and Italy has stopped paying altogether.

On June 8th the United Nations meets to discuss what to do next. Those who see the UN as a mere talking-shop should remember that its first meeting on AIDS launched the Global Fund. It is still a long haul. But AIDS can be beaten. A plague that 30 years ago was blamed on man’s iniquity has ended up showing him in a better, more inventive and generous light.